The use of video laryngoscopy outside the operating room: A systematic review

This study aimed to describe how video laryngoscopy is used outside the operating room within the hospital setting. Specifically, we aimed to summarise the evidence for the use of video laryngoscopy outside the operating room, and detail how it appears in current clinical practice guidelines. A literature search was conducted across two databases (MEDLINE and Embase), and all articles underwent screening for relevance to our aims and pre-determined exclusion criteria. Our results include 14 clinical practice guidelines, 12 interventional studies, 38 observational studies. Our results show that video laryngoscopy is likely to improve glottic view and decrease the incidence of oesophageal intubations; however, it remains unclear as to how this contributes to first-pass success, overall intubation success and clinical outcomes such as mortality outside the operating room. Furthermore, our results indicate that the appearance of video laryngoscopy in clinical practice guidelines has increased in recent years, and particularly through the COVID-19 pandemic. Current COVID-19 airway management guidelines unanimously introduce video laryngoscopy as a first-line (rather than rescue) device.


Introduction
Tracheal intubation occurring outside the operating room (OR) typically involves a critically unwell patient. These intubations occur predominantly in the emergency department (ED) or intensive care unit (ICU), but may also involve a deteriorating patient on a hospital ward. Intubation outside the OR presents greater difficulty to the airway, with a significantly increased incidence of adverse events and risks to patient safety [1,2]. Reasons for this include availability of skilled staff in an emergency, case mix and working environment [3]. In the recent INTUBE study, 45.2% of intubations outside the OR experienced at least 1 major adverse periintubation event and over 3% were complicated by cardiac arrest [2]. First-pass intubation success is particularly important in the critically ill and is associated with improved hospital survival in this group [2]. As the number of intubation attempts increases, so too does the incidence of adverse events and hospital mortality [2,4]. As such, every effort should be made to maximise first-pass intubation success outside the OR. Strategies to increase first-pass success include choice of an experienced clinician (such as a consultant anaesthetist), positioning, adequate muscle relaxation, and use of equipment [5][6][7]. Specifically, airway operators must consider whether to use direct laryngoscopy (DL) or video laryngoscopy (VL). VL displays the glottis on an external monitor via a camera attached to the device blade, without requiring alignment of the oral-pharyngeal-tracheal axes. Furthermore, because the glottis is displayed on an external monitor, VL allows supervising clinicians real-time view, allowing them to provide tailored guidance to trainees [8,9]. Historically, VL is often referred to in difficult airway management algorithms as a powerful rescue tool to be employed when initial intubation attempts are unsuccessful [10,11]. Recently, the use of VL has increased, which is likely due to multiple factors including the improved glottic view that VL offers compared to DL, and its increased availability and affordability [12,13]. There has also been an increase in the uptake of VL during the COVID-19 pandemic, with many airway management guidelines now recommending VL as a first line (rather than rescue) device [6,7,13]. Within the OR, it has been found that VL may reduce the number of failed intubations, particularly among patients presenting with a difficult airway [14]. However, there has been conflicting results of early VL studies outside OR. There is no current consensus on the use of VL outside the OR; specifically, whether it should be used ahead of DL, whether it is best used by trainees, consultants or both, and what benefit to patient outcomes it may offer. Existing systematic reviews on the use of VL were conducted prior to the COVID-19 pandemic, and do not evaluate the most recent evidence on the use of VL outside the OR. This study was designed to conduct an up-to-date review of the existing literature on how VL is used outside the OR. Specifically, it aims to (1) search for and summarise the recent evidence for the use of VL outside the OR and (2) describe how VL appears in current clinical practice guidelines for airway management outside the OR.

Materials and methods
A structured literature search adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) recommendations and was registered with PROSPERO [15]. A search was conducted across two databases (MEDLINE and Embase) on September 8, 2021, looking at the use of VL outside the OR. Keywords searched were "laryngoscopy" + "video recording", "video laryngoscopy", "video assisted laryngoscopy", "penta airway", "king vision" or "mcgrath mac", in conjunction with "intensive care units", "critical illness", "ICU(s)", "emergency department", "emergency service/hospital" or "critically ill". Pre-defined exclusion criteria were studies not in English, not in ED/ICU/ward based/critically ill settings, prehospital settings, simulation studies, involving students, conference abstracts only, commentary/editorials or neonatal/paediatric papers. Furthermore, articles were limited to those published between 1 January 2011-8 September 2021.
All resulting references underwent title and abstract screening using Covidence software (Veritas Health Innovation Ltd, Melbourne, Victoria). Articles were initially screened by a single author, and any articles that were not clearly able to be included or excluded were then discussed amongst the team of authors. Full texts were then extracted and screened by two authors for relevance to pre-defined inclusion and exclusion criteria (Fig 1).
Both clinical practice guidelines and consensus statements (for both intubation and advanced life support/cardiopulmonary resuscitation) were included. This yielded both primary and secondary research papers discussing the use of VL outside the OR (ED, ICU and ward-based setting). As this is a review article, we limited citations of other review articles or meta-analyses to the introduction and discussion and only primary data was used in our descriptive analysis.
Clinical practice guidelines and consensus statements were identified and tabulated (Table 1). Articles discussing the use of VL outside the OR were identified and tabulated separately, with Table 2 detailing interventional studies and Table 3 detailing observational studies. Descriptive analysis was performed to assess how VL is used outside the OR, what the evidence is for its use outside the OR and the appearance of VL in current clinical practice guidelines. The quality of included papers was assessed using the Critical Appraisal

PLOS ONE
Video laryngoscopy outside the operating room

Search results
Following duplicate removal, our search generated 890 articles. Articles then underwent title and abstract screening and full text screening for relevance to our aims and exclusion criteria. This yielded a total of 64 articles to be included in our review. Guidelines not intended for use outside the OR, or guidelines that did not make mention of VL, were excluded. The 64 papers included 14 clinical practice guidelines or consensus statements (Table 1), 12 interventional studies including RCTs (Table 2) and 38 observational studies on the use of VL outside the OR (Table 3).

Quality assessment
The quality of the included studies was primarily assessed used CASP tool [16]. Cross-sectional studies were assessed using the MERSQI tool [17]. Overall, the quality of included research was found to be low-moderate.

Included airway guidelines
Guidelines were published from a range of countries as shown in Table 1. Table 1 also details data on society/expert group endorsement of the guidelines, methodology for guideline development, intended patient group, recommendations, and evidence base. How is VL mentioned within guidelines?. Safe Airway Society guidelines for airway management of COVID-19 patients from Australia and New Zealand were the first to recommend VL as the first line device in COVID-19 patients when the airway operator is proficient in its use [6]. The Macintosh video laryngoscope and the hyperangulated video laryngoscope are the two types of VL referenced in this guideline. Guidelines from Cook et al. 2020, which come from consensus among Difficult Airway Society, the Association of Anaesthetists of the Intensive Care Society, and Faculty of Intensive Care Medicine and the Royal College of Anaesthetists, recommended that laryngoscopy be undertaken with the device that is most likely to achieve prompt first-pass success in patients with COVID-19 [7]. This guideline states that in most fully trained airway professionals, this is likely to be VL. Guidelines from Nasa et al. 2021, recommend considering VL for intubation of COVID-19 [22]. The guideline does not discuss a specific type of VL. Guidelines from Sharma et al. 2020, which are intended for use in COVID-19 patients requiring emergency endovascular treatment, state that VL should be used for intubation [26]. Guidelines [10]. All other included guidelines recommended early use of VL or the use of VL, rather than only as a rescue device.
Overall intubation success. Overall intubation success rate was a measured outcome in four of the included studies, with none of these reporting a difference in overall intubation success using VL compared to DL [35,62,63,67]. Glottic view. There were 8 included studies that assessed glottic view as an outcome measure. Of these, 7/8 (87.5%) report that VL is associated with improved glottic view compared to DL [31,34,42,44,54,65,66]. Carlson et al. reported that there was no difference in glottic view when using VL compared to DL [47].
Oesophageal intubation rate. There were 4 studies that looked at rate of oesophageal intubations, with 100% of these reporting less oesophageal intubations with VL compared to with DL [36,63,66,67].
Incidence of difficult intubation. Difficult intubation was an outcome measure in 2 of the included studies, both of which found that the incidence of difficult intubation was less with VL compared to DL [28,36].
Complications of intubation. There were eight included studies that discussed complications of intubation using VL. Overall, the results of these studies were varied. Four (50%) of these studies found that there was a difference between VL and DL in terms of complication rates [37,39,40,57], whereas four (50%) did not [28,29,34,35].
Clinical outcomes. Clinical outcomes including hospital length of stay and in-hospital mortality rates were measured in only three included studies. There was no statistically significant difference in hospital length of stay, in-hospital mortality or overall mortality found in these studies [29,31,34].

Discussion
This study aimed to provide an up-to-date review of the role of VL in intubation of the critically ill outside the OR. We identified 64 research papers from the past 10 years on the use of VL outside the OR, including 14 clinical practice guidelines.
In terms of first-pass success, some of our included papers (n = 13) showed increased first pass success with VL compared to DL; however, a similar number of papers (n = 11) showed no difference in first-pass success between VL and DL. Weng et al. (2020) found that VL was associated with improved first past success amongst non-attending physicians, but this difference was not seen amongst attending physicians [9]. This suggests that the usefulness of VL in helping to achieve first pass success may be operator dependent. This finding is in keeping with the existing literature, with a review article and meta-analysis from Arulkumaran et al. (2018) demonstrating that first-pass success was increased when VL was used in ICU and amongst novice/trainee clinicians [8]. Furthermore, a review article from Howson et al. (2020) also showed that first-pass success was higher with VL compared to DL in junior operators, but the difference was not seen amongst senior operators [77].
Although some results suggest that VL may improve first-pass intubation success, our results indicate that VL is yet to be shown to improve overall intubation success. We found that VL is likely to improve glottic view, and reduce the incidence of oesophageal intubations; however, the degree to which this view is improved and how this improves clinical outcomes remains unclear. Further research is required to directly determine this.
Most worthy of discussion when reflecting on both first pass success and improved glottic view with VL is the type of VL blade used. There has been a move in recent years towards a Macintosh blade by most VL manufacturers, with an increased focus on the use VL with a hyperangulated blade (HAVL). The papers included in this study have a heterogenous group of video laryngoscopes and blades. HAVL may indeed further improve glottic view, but firstpass success may differ depending on the volume of practice and training in HAVL by the operator [43,78]. Future research should focus on these outcomes with the use of VL, whilst drawing a distinction between conventional VL blades and HAVL, as well as the use of HAVL in novice versus experienced operator hands.
Our results show that the frequency of VL use outside the OR appears to be increasing in recent years, and particularly through the COVID-19 pandemic. This may be due to VL becoming more affordable and more readily available in both the ICU and ED. Although the exact frequency of VL use outside the OR is uncertain, some studies in our review suggest that the frequency of VL use has increased dramatically during the COVID-19 pandemic [2]. This is likely in response to published clinical practice guidelines on airway management for COVID-19 patients outside the OR unanimously supporting the use of VL in COVID-19 patients, and the perception of safety presented by the increased distance between the airway operator and the patient that VL offers [6]. However, as the COVID-19 pandemic has evolved, we have learnt that the virus is transmitted more by aerosols than my contact, so increased distance between the patient's airway and the airway operator is perhaps less protective than initially thought. Furthermore, VL is recognised as a powerful training tool, as it allows a supervisor to view to airway in real time and provide real time guidance to a trainee airway operator [9].
Our results were varied in terms of the impact of VL on complications of intubation. Some studies showed that complications such as severe hypoxemia were lower when VL was used, whilst others showed that this complication actually increased with the use of VL. There were 3 studies that looked at clinical outcomes for patients including hospital length of stay and inhospital mortality rates. There was no statistically significant difference in hospital length of stay, in-hospital mortality or overall mortality found in our included studies. However, the recently published INTUBE study has since also demonstrated an increased likelihood or firstpass success through the use of VL outside the OR [2]. This success correlated with a reduced primary adverse event outcome, being a composite outcome measure that included cardiovascular instability (42.6%), severe hypoxemia (9.3%) and cardiac arrest in 3.1%. Patients in that study with a primary adverse event had an increased hospital mortality (40.7% vs 26.3%) [2]. This should prompt ongoing research to look at specific patient outcomes associated with the use of VL in this patient group.
The primary limitation of this paper is the heterogenous nature of the included papers. Research varied in terms of country of publication, setting, patient group, airway operator(s), study design and type of VL assessed. Specifically, observational studies are analysed alongside RCTs and other interventional studies, which limits the strength of our conclusions. Outcome measures also varied significantly. Most included studies are observational and have a small sample size. In addition, most of the included clinical practice guidelines do not provide a detailed description of their evidence base, or their methodology for guideline development. They also do not describe the use of the same VL manufacturer or blade type. Limited research has been described specifically on the use and benefit of HAVL in this group.

Conclusion
Ultimately, our results suggest that the use of VL outside the OR has increased in recent years, and particularly through the COVID-19 pandemic. The early use of VL is recommended in most published clinical practice guidelines and is unanimously recommended for management of COVID-19 intubations. It appears that VL is likely to improve glottic view and decrease incidence of oesophageal intubations; however, it remains unclear as to how this contributes to first-pass success. Within the limitations of our research, we found that VL has yet to show significant improvement in overall intubation success or clinical outcomes such as mortality outside the OR. More directed research is required to further characterise the use of VL outside the OR, the type of blade used and the clinical outcomes associated with its use.